In the drilling industry, in the absence of downhole measurements, the hookload and surface torque measurements are used to calculate weight on the bit and the bit torque. To apply weight on the bit, it is required to apply some portion of drillstring weight on the bit. The weight on the bit is calculated based on the difference between the hookload values when drillstring is off and on bottom. The surface weight on the bit could be the true value, if the well is vertical and the axial friction force between drillstring and the wellbore is negligible. When the well deviate from vertical straight line, the surface and downhole weight on the bit may not be the same due to axial friction force between drillstring and the wellbore. The same happens for bit torque calculation. The bit torque is estimated from difference between surface torque measurements while drilling bit is off and on bottom. An improved method of calculating downhole weight on bit and using this information in the drilling process is required.
Drilling data has been used in rate of penetration (ROP) models to predict rock strength since the 1980s. The development of ROP models has been ongoing for decades and since the 1980s there exist ROP models for tricone, PDC and natural diamond bits. These ROP models have mostly been verified for some bit types with laboratory drilling data and in some cases data collected from the field.